A Systematic Approach for Analyzing the Manufacturability of Machined Parts

The ability to quickly introduce new quality products is a decisive factor in capturing market share. Because of pressing demands to reduce lead time, analyzing the manufacturability of the proposed design has become an important step in the design stage. This paper presents an approach for analyzing the manufacturability of machined parts. Evaluating the manufacturability of a proposed design involves determining whether. or not it is manufacturable with a given set of manufacturing operationsand if so, then finding the associated manufacturing efficiency. Since there can be several different ways to manufacture a proposed design, this requires us to consider different ways to manufacture it, in order to determine which one best meets the design and manufacturing objectives. The first step in our approach is to identify all machining operations which can potentially be used to create the given design. Using these operations, we generate different operation plans for machining the part. Each time we generate a new operation plan, we examine whether it can produce the desired shape and tolerances, and calculate its manufacturability rating. If no operation plan can be found that is capable of producing the design, then the given design is considered unmachinable; otherwise, the manufacturability rating for the design is the rating of the best operation plan. We anticipate that by providing feedback about possible problems with the design, this work will help in speeding up the evaluation of new product designs in order to decide how or whether to manufacture them. Such a capability will be useful in responding quickly to changing demands and opportunities in the marketplace. (Also cross-referenced as UMIACS-TR-93-105

A Planning Approach to Declarer Play in Contract Bridge

Although game-tree search works well in perfect-information games, it is less suitable for imperfect-information games such as contract bridge. The lack of knowledge about the opponents' possible moves gives the game tree a very large branching factor, making it impossible to search a significant portion of this tree in a reasonable amount of time. This paper describes our approach for overcoming this problem. We represent information about bridge in a task network that is extended to represent multi-agency and uncertainty. Our game-playing procedure uses this task network to generate game trees in which the set of alternative choices is determined not by the set of possible actions, but by the set of available tactical and strategic schemes. We have tested this approach on declarer play in the game of bridge, in an implementation called Tignum 2. On 5000 randomly generated notrump deals, Tignum 2 beat the strongest commercially available program by 1394 to 1302, with 2304 ties. These results are statistically significant at the alpha = 0.05 level. Tignum~2 searched an average of only 8745.6 moves per deal in an average time of only 27.5 seconds per deal on a Sun SPARCstation 10. Further enhancements to Tignum~2 are currently underway. (Also cross-referenced as UMIACS-TR-95-85

Complexity Results for HTN Planning

(Also cross-referenced as ISR-TR-95-10) Most practical work on AI planning systems during the last fifteen years has been based on hierarchical task network (HTN) decomposition, but until now, there has been very little analytical work on the properties of HTN planners. This paper describes how the complexity of HTN planning varies with various conditions on the task networks, and how it compares to STRIPS-style planning. (Also cross-referenced as UMIACS-TR-94-32

Complexity, Decidability and Undecidability Results for Domain-Independent Planning: A Detailed Analysis

In this paper, we examine how the complexity of domain-independent planning with STRIPS-like operators depends on the nature of the planning operators. We show conditions under which plannning is decidable and undecidable. Our results on this topic solve an open problem posed by Chapman [4], and clear up some difficulties with his undecidability theorems. For those cases where planning is decidable, we show how the time complexity varies depending on a wide variety of conditions: . whether or not function symbols are allowed; . whether or not delete lists are a]]owed; . whether or not negative preconditions are allowed; . whether or not the predicates are restricted to be propositional(i.e., 0-ary); . whether the planning operators are given as part of the input to the planning prob]em, or instead are fixed in advance. (Also cross-referenced as UMIACS-TR-91-154

Semantics for HTN Planning

(Also cross-referenced as ISR-TR-95-9) One big obstacle to understanding the nature of hierarchical task network (HTN) planning has been the lack of a clear theoretical framework. In particular, no one has yet presented a clear and concise HTN algorithm that is sound and complete. In this paper, we present a formal syntax and semantics for HTN planning. Based on this syntax and semantics, we are able to define an algorithm for HTN planning and prove it sound and complete. We also develop several definitions of expressivity for planning languages and prove that HTN Planning is strictly more expressive than STRIPS-style planning according to those definitions. (Also cross-referenced as UMIACS-TR-94-31

A Geometric Algorithm for Finding the Largest Milling Cutter

In this paper, we describe a new geometric algorithm to determine the largest feasible cutter size for2-D milling operations to be performed using a single cutter. In particular:1. We give a general definition of the problem as the task of covering a target region without interfering with anobstruction region. This definition encompasses the task of milling a general 2-D profile that includes bothopen and closed edges.2. We discuss three alternative definitions of what it means for a cutter to be feasible, and explain which of thesedefinitions is most appropriate for the above problem.3. We present a geometric algorithm for finding the maximal cutter for 2-D milling operations, and we show thatour algorithm is correct

Selecting Flat End Mills for 2-1/2D Milling Operations

The size of milling cutter significantly affects the machining time. Therefore, in order to perform milling operations efficiently, we need to select a set of milling cutters with optimal sizes. It is difficult for human process planners to select the optimal or near optimal set of milling cutters due to complex geometric interactions among tools size, part shapes, and tool trajectories. In this paper, we give a geometric algorithm to find the optimal cutters for 2-1/2D milling operations. We define the 2-1/2D milling operations as covering the target region without intersecting with the obstruction region. This definition allows us to handle the open edge problem. Based on this definition, we introduced the offsetting and inverse-offsetting algorithm to find the coverable area for a given cutter. Following that, we represent the cutter selection problem as shortest path problem and discuss the lower and upper bond of cutter sizes that are feasible for given parts. The Dijkstra's algorithm is used to solve the problem and thus a set of cutters is selected in order to achieve the optimum machining cost. We believe the selection of optimum cutter combination can not only save manufacturing time but also help automatic process planning

Integrating DFM with CAD through Design Critiquing

The increasing focus on design for manufacturability (DFM) in research in concurrent engineering and engineering design is expanding the scope of traditional design activities in order to identify and eliminate manufacturing problems during the design stage. Manufacturing a product generally involves many different kinds of manufacturing activities, each having different characteristics. A design that is good for one kind of activity may not be good for another, for example, a design that is easy to assemble may not be easy to machine. One obstacle to DFM is the difficulty involved in building a single system that can handle the various manufacturing domains relevant to a design. In this paper we propose an architecture for integrating CAD with DFM. As the designer creates a design multiple critiquing systems analyze its manufacturability with respect to different manufacturing domains such as machining, fixturing, assembly, and inspection. Using this analysis, each critiquing system offers advice about potential ways of improving the design and an integration module mediates conflicts among the different critiquing systems in order to provide feedback to improve the overall design. We anticipate that this approach can be used to build a multi-domain environment that will allow designers to create higher-quality products that can be more economically manufactured. This will reduce the need for redesign and reduce product cost and lead time. (Also cross-referenced as UMIACS-TR-94-96

Manufacturing-Operation Planning Versus AI Planning

Although AI planning techniques can potentially be useful in several manufacturing domains, this potential remains largely unrealized. Many of the issues important to manufacturing engineers have now seemed interesting to AI researchers -- but, in order to adapt AI planning techniques to manufacturing, it is important to address these issues in a realistic and robust manner. Furthermore, by investigating these issues, AI researchers may be able to discover principles that are relevant for AI planning in general. As an example, in this paper we describe the techniques for manufacturing- operation planning used in IMACS (Interactive Manufacturability Analysis and Critiquing System). We compare and contrast them with the techniques used in classical AI planning systems, and point out that some of the techniques used in IMACS may also be useful in other kinds of planning problems. (Also cross-referenced as UMIACS-TR-95-3